A bit of a letdown. Started out promising, with the trademark Greene conversational style and the relatively-interesting patchwork parallel universes. Somewhere toward the middle and the landscape multiverse, the book became quite plodding. I don't know if it's that the subject matter is just so dense that not even Greene can enliven it or what, but that section was a chore to get through.
Eventually things got better, and we ended up on a higher note, so the book was not a complete loss. The discussion of Holograms and the Quantum Multiverse were interesting enough.
I was pleasantly surprised to see the chapter on simulated universes, and the implications of same. It wasn't the sort of thing that came to mind when I heard of this book about parallel universes, but it was definitely worth consideration.